I've been trying to unbrick my Kindle 4 using Kubrick. It seemed to work after a few tries. Got through the whole process and it booted apparently fine after that, but it froze again almost immediately. This happened a few times, until it just froze for good at the booting screen (about a third of the progress bar under the tree).

It's not the battery, because it has a brand new one which worked in the previous unbricking processes using Kubrick, and I charge it from the wall for many hours as is recommended before every attempt.